Optical scanners operate by imaging an object (e.g. a document) with a light source, and sensing a resultant light signal with an optical sensor array (also called a photosensor array herein). Each optical sensor or photoreceptor in the array generates a data signal representative of the intensity of light impinged thereon for a corresponding portion of the imaged object. The data signals from the array sensors are then processed (typically digitized) and stored in a temporary memory such as a semiconductor memory or on a hard disk of a computer, for example, for subsequent manipulation and printing or display, such as on a computer monitor. The image of the scanned object is projected onto the photosensor array incrementally by use of a moving scan line. The moving scan line is produced either by moving the document with respect to a scan assembly, or by moving the scan assembly relative to the document. Either or both of these methods may be embodied in a flat bed scanner, multi-function printer, or any scanner having manual and automatic feed capabilities.
One type of scanner is the contact image sensor (CIS) scanner. A CIS scanner includes a contact image sensor having a length that is substantially equal to the width of the scanning region. The photosensors in a CIS are substantially the same size as the pixel resolution of the scanner. Because the photosensors in the CIS relatively large, a low power light source (such as one or more LED's) is sufficient to provide enough illumination in the scan line image region. The CIS has a short depth of field and is typically mounted beneath the transparent platen upon which the document is placed. One or more rollers in the CIS carriage are biased against the bottom of the transparent platen so that the CIS is always at substantially the same distance from the top of the transparent platen.
Photosensors in a CIS scanner photosensor array are aligned in a direction parallel to the longitudinal axis of the scan line image which is projected thereon. The direction perpendicular to the photosensor array direction is referred to herein as the “scan” direction (i.e., the direction of movement of a document or of the photosensor array for scanning of the image).
At any instant when an object is being scanned, each photosensor in the photosensor array has a corresponding area on the object which is being imaged thereon. This corresponding area on the scanned object is referred to herein as a pixel. An area on a scanned object corresponding to the entire extent of the photosensor array is referred to herein as a scan line. For descriptive purposes, a scanned object is considered to have a series of fixed adjacently positioned scan lines. Further, scanners are typically operated at a scan line sweep rate such that one scan line width is traversed during each sampling interval.
When working with cut sheet print media, a copying, scanning or multifunction printing apparatus can provide automatic document feed, as well as manual document placement capabilities. An automatic document feeder (ADF) mechanism is capable of automatically loading and unloading single sheets sequentially to a functional station where the apparatus performs an operation, e.g., sequentially scanning the fed document sheets for copying, faxing, displaying on a computer monitor, or the like. Following the operation, the ADF then off-loads a sheet and feeds the immediately following sheet of the document to the functional station. A sequential flow of sheets by the ADF and positioning without the necessity of manual handling reduces the time required to accomplish the complete functional operation. An ADF can be designed to scan single-sided originals or two-sided originals.
Each document fed into the ADF is conveyed to an automatic scanning region where the document is scanned by a photosensor array and then the document is conveyed to a point outside the ADF, such as a document output tray. During ADF operation, the photosensor array remains fixed at the automatic scanning region “reading” or scanning the image as the document is conveyed past the scanning point by the ADF. During manual scanning, the document lays flat on and covers a portion of the flat platen while the photosensor array is moved under the platen the length (or width) of the document to read or scan the document. Conventional scanners having an ADF use a first motor to move the document during ADF operation and a second motor to move the photosensor array during manual scanning
U.S. Pat. No. 7,948,663 discloses a scanning apparatus having a single motor that is shared between moving the document during ADF operation and moving the photosensor array during manual scanning. This is possible because the two types of motion do not occur at the same time. During ADF operation the document is moved, and during manual scanning the photosensor array is moved. This solution saves the cost of a motor. However, selectively transmitting power from the single motor to the ADF or to the photosensor array requires some complexity in the gearing.
A need exists for a scanning apparatus with ADF capability, either as a standalone scanner or incorporated as part of a multifunction printer, having cost advantages relative to the conventional scanner having an ADF, but without the power transmission complexities associated with sharing a single motor between the ADF and the photosensor array.